Fluoroplastic encapsulated electrical resistance heaters

ABSTRACT

An electrical resistance immersion heater in which a resistance heater unit including an attached cold extension is encapsulated in a thin fluoroplastic sheathing. The cold extension and heater are capable of being formed in various shapes, the end of which is enclosed by means of a molded terminal ending.

United States Patent McArn I 1151 3,663,799 1 51 May 16, 1972 541FLUOROPLASTIC ENCAPSULATED ELECTRICAL RESISTANCE HEATERS [72] Inventor:Angus H. McArn, PO. Box 11127, Pitt- ,sburgh, Pa. 15234 [22] Filed: Oct.12, 1970 [21] Appl. No.: 79,885

52 u.s.c1 ..219 523,174 75,219/52s, 219/541, 219/544, 219 549, 338/214,338/274 51 1111.01. ..H05b3/06 5s FieldofSearch..219/523,528,535,549,552, 219/437, 415, 541, 544; 33s 273-274, 214,212;

[56] References Cited UNITED, STATES PATENT S 2,982,932 5/1961 Morey,..219/528X 3,225,321 12/1965 Walter ..219/523 X 3,441,893 4/1969 Gordonet al. ..338/214 X 2,888,547 5/1959 Saper ..219/523 3,045,102 7/1962Fessenden .....2l9/528 3,097,288 7/1963 Dunlap 219/528 X 3,113,28412/1963 Van lnth0udt.. ..338/274 3,257,498 6/1966 Kahn 1 74/75 3,356,835l2/l 967 Watson ..219/549 Primary Examiner-Velodymyr Y. MayewskyAttorney-Buell, Blenko & Ziesenheim [57] ABSTRACT An electricalresistance immersion heater in which a resistance heater unit includingan attached cold extension is encapsulated in a thin fluoroplasticsheathing. The cold extension and heater are capable of being formed invarious shapes,

the end of which is enclosed by means of a molded terminalending.

2 Claims, 2 Drawing Figures Patented May 16, 1972 3,663,799

I/VVENTOR. Angus H. McArn gag m HIS ATTORNEYS FLUOROPLASTIC ENCAPSULATEDELECTRICAL RESISTANCE HEATERS My invention relates to electrical heatersand, in particular, to electrical heaters of the immersion type.

Presently, most electrical immersion heater units utilize a coil ofresistance wire which can be free standing or wound about a hollow tubeor core of mica or other ceramic material; see, e.g., U.S. PatsNo.1,365,978. The winding of resistance wire is then usually encased in aliquid proof container such as metal, fused quartz, graphite, or glass.A background of the various prior art heaters of the immersion type andtheir various features by examination of the following non-exhaustivelist of US. Patents: U.S. Pat. Nos. 3,476,916; 3,340,382; 3,399,295;3,107,290; 2,888,547; 274,843; 2,726,316; and 2,727,979.

Substantial advantages have been made in design and fabrication ofimmersion type heaters, but their use has been greatly limited becauseof their inability to satisfactorily operate in a variety of differentenvironments such as highly caustic or acidic solutions. Heatersdesigned to operate in highly corrosive solutions, such as encapsulatedglass, fused quartz or graphite heaters, as well as various metal alloysgenerally include one or more of the following deficiencies: 1) they areextremely fragile, (2) they have limited corrosion resistant parameters,i.e. a limited pH range, etc., (3) they are extremely difficult tofabricate and accordingly, extremely expensive, or (4) they areextremely difficult to clean.

- I have been able to overcome many if not all of the deficiencies foundin the prior art immersion type heaters with my present invention. 1provide an immersion type heater capable of being formed into a numberof different configurations for various applications, and which isparticularly well adapted for use in highly corrosive solutions. Theheater of the present invention is break resistant as well as beingadaptable to relatively simple fabrication methods. Moreover, the heaterunit is extremely easy to clean.

In general, I provide an immersion heater including a cold extensionboth of which are tightly encapsulated in an expanded thin fluoroplasticsheathing. Because of the extremely stable carbon-fluoride bond whichrenders the fluoroplastics chemically inert to a great variety ofchemical solutions, the heater is operable in highly corrosivesolutions. By the proper application of one or more fluoroplastics to anelectrical heater, I am able to provide an extremely flexible andadaptable immersion heater.

Other advantages and features of my invention will become apparent froma perusal of the following detailed specification taken in connectionwith the following drawings:

FIG. 1 is an elevation in partial section of the immersion heater, coldextension and molded junction; and

FIG. 2 is a plan view of a shallow tank immersion heater design.

Referring to FIG. 1, immersion heater comprises an electrical resistanceheater unit 12. Heater 12 can be a commercially available unit and assuch usually includes a resistive coil 13 having a pair of leads l5 and16. Heater 12 also includes a casing 17 generally comprising adeformable light metal or similar material. Leads 15 and 16 areconnected through a cold extension 21 to a molded juncture or terminalfor con-. nection with an outside power source by means of wires 26 and27 respectively. The outside power source may also be connected with athermo couple or other thermostatic device for temperature regulation ofthe solution in which the heater is placed and which does not comprise apart of this invention.

To each end of heater 12 is a fixed a cold extension 21 usuallycomprising a hollow metal tube having a length sufficient for formationinto any desired configuration. The cold extension is mounted or affixedto the cold end 22 of the heater 12 by any suitable metallurgical ormechanical means. By utilization of standard heaters, it is, therefore,possible to design and fabricate a very large number of sizes andconfigurations of immersion heaters by selection of varying sizes ofcold extensions. The cold extension is filled with an insulatingmaterial 23 such as an epoxy or a magnesium oxide.

The heater and cold extension are then encapsulated with a sheathing ofexpanded fluoroplastic 20. The thin fluoroplastic coating, e.g.,fluorinated ethylene propylene is preferably placed over both extensionsand the heater as single piece to provide a fluid-tight barrier. Thesheathing is tightly drawn against heater unit to maximize heattransfer. The heater including the cold extensions, with thefluoroplastic sheathing is then formed intothe desired configuration,e.g., F IG. 2.

At the ends of the cold extension, FIG. 2, wires 26 and 27 are connectedwith a pair of leads going to a source of current, or alternatively,lead directly to connection with power source. This connection is thenincluded within or, alternatively, the wires pass through terminal 25which is molded to seal the cold extension as well as the connection orwires. Terminal 25 provides, therefore, a seal against fluid and isuseful in supporting the entire unit on the edge of fluid tank, etc.

The temperature of the resisting unit 12 must be maintained below themaximum continuous operating temperature of the fluoroplastic.Accordingly, the heat flux of the unit 10 is a function of the heattransfer rate of the fluoroplastic covering. For example, the heattransfer rate of fluorinated ethylene propylene (FEP) is approximately6(10) call(sec)(cm )(c/cm). This is equivalent to 35.2 (10)watts/(in)(F./in). Accordingly, for an 0.015 inch thick sheath of FEP,the temperature drop would be approximately 4.25 F./w./in and operatingat 30 wlin a temperature gradient of 127 F. would be established. Thus,based on the heat transfer of F .E.P., a 0.015 inch sheathed immersionheater 10 with heater unit 12 operating at 450 F. maximum continuoustemperature would be capable of maintaining a solution at approximately323 F.

Experiments have confirmed the heat transfer rates and establish theoperability of these heaters. Heaters with an 0.012 inch thick FEPsheathing were operated for a continuous period of 562 hours with asolution temperature of l-l90 F. Other heaters of varying sizessheathing thickness have been operated for over 6 months without anyfailure. These heaters are extremely resistant to corrosion failures andare easy to clean. For example, 20 w/in heaters having 0.020 inch F E?sheath have continuously operated F. H SO for over 280 hours without anyfailure.

While I have shown a presently preferred embodiment of my invention, itmay otherwise be described as set forth in the following claims.

I claim:

1. An electrical resistance immersion heater comprising an electricalresistance heating means including a deformable thin metallic housingtherefor; a pair of cold extensions one attached to each end of saidhousing and adapted to carry electrical wire therethrough to connectsaid resistance means with a power source; at least one molded terminalat which each cold extension terminates; and an outer fluoroplasticsheathing tightly covering said housing and said cold extension indirect contact therewith whereby the housing and extension are renderedfluid resistant, said sheathing being from between about 0.012 and 0.020inches in thickness.

2. An electrical resistance immersion heater as set forth in claim 1wherein said pair of cold extensions, one at each end of said housingcome together in a contiguous relationship.

1. An electrical resistance immersion heater comprising an electricalresistance heating means including a deformable thin metallic housingtherefor; a pair of cold extensions one attached to each end of saidhousing and adapted to carry electrical wire therethrough to connectsaid resistance means with a power source; at least one molded terminalat which each cold extension terminates; and an outer fluoroplasticsheathing tightly covering said housing and said cold extension indirect contact therewith whereby the housing and extension are renderedfluid resistant, said sheathing being from between about 0.012 and 0.020inches in thickness.
 2. An electrical resistance immersion heater as setforth in claim 1 wherein said pair of cold extensions, one at each endof said housing come together in a contiguous relationship.